I highly recomend this one posted by Klinkers
in the link gonehuntingagain posted. It is "cut and paste"able directly into a spreadsheet for making drop charts. It is VERY flexible. You can ask for your drops by the 1 yard increment if you want or you can ask it for your drops and windage in 3 different forms. Heck, you can even include or remove any or all of the data collumns it calculates.
Way cool stuff.
P.S. You don't have to log in to use the site. Just click on "Load definition" to start entering your info.